Effects of amiloride, applied extracellularly, on mechano-electrical transduction (MET) currents were investigated in dissociated hair cells of a chick with a whole-cell patch-electrode voltage clamp technique. Amiloride blocked the MET channel. The blocking was reversible and was both dose and voltage dependent and specific to the MET channel. The voltage-dependent Ca2+ channel of the basolateral membrane was not affected within the concentration range studied (up to 0.7 mM). 2. The limiting conductance of the MET at large negative membrane potentials decreased with increasing amiloride concentration. A dose-response relationship of the relative MET conductance (defined as the ratio of the MET channel conductance in the presence of amiloride to that without) at membrane potentials more negative than -50 mV had a Hill coefficient of 1, and a dissociation constant (KD) of 5 x 10(-5) M. 3. When amiloride was applied, the MET conductance increased as the membrane was depolarized, and the limiting value at positive membrane potentials was close to that of the control. The relationship between the relative MET conductance and the membrane potential was S-shaped. The conductance vs. voltage relationship was shifted in a positive direction along the voltage axis as the amiloride concentration was increased. 4. The blocking effect of amiloride on the MET channel was apparently independent of the mechanical gating of the channel. The voltage-independent block at or near the resting membrane potential and a voltage-dependent lifting of the block at depolarized membrane potentials could be explained quantitatively by a kinetic model which postulates one blocked state and two open states which have different amiloride affinities.
